1. Field of the Invention
The present invention relates to a path network for carrying out communications using one or more working paths and one or more protection paths between nodes, and more particularly to a method for operating such a path network which is capable of dealing with a bandwidth increase request resulting from an abrupt traffic variation.
2. Description of the Background Art
Conventionally, in a path network where communications are carried out by using working paths and protection paths and these paths are managed by a network management system, when there is a bandwidth increase request due to an increase of traffic or a convenience of management, the bandwidth is increased by the network management system by searching for idle paths among the working paths as well as idle paths among the protection paths, and opening any idle paths that are found by the search to traffic.
Here, a path network is a network which employs a transmission network hierarchy (three hierarchical levels) in a frame structure as a characteristic of SDH (Synchronous Digital Hierarchy), which is defined along with a channel network and a media network, which is not dependent on any channels and transmission media, which is shared by various services in general, and which constitutes a unit of operation in a transmission path network. Also, an optical path is a unit of operation for each wavelength in a transmission path network.
In general, in the path network, the working path and the protection path are used to transmit the same signals between the same nodes via different routes such that the protection signals transmitted by the protection path can be utilized whenever the working path fails.
FIG. 1 and FIG. 2 show exemplary configurations of a conventional path network which respectively indicate an initial state before the path number change and a state after the path number change. FIG. 3 is a flow chart for the operation of a network management system in a conventional path number changing procedure.
In FIG. 1 and FIG. 2, the path network comprises nodes 1–5 (node A to node E), a network management system (OpS) 6, working paths indicated by solid lines, protection paths indicated by dashed lines, and network management communication paths indicated by dotted chain lines. FIG. 1 shows an initial state of an ordinary operation state, where two working paths are connected from a node A 1 to a node E 5 through a node B 2 and a node C 3. In such an initial state, a bandwidth increase request will be generated when traffic between the node A 1 and the node E 5 is increased or when it becomes necessary for a convenience of management as in the case of carrying out a construction between the node A 1 and the node E 5. The network management system 6 refers to a network configuration information to search for idle paths among the working paths as well as idle paths among the protection paths in response to the request, and if idle paths are found, the network management system 6 sends a command for opening a path to nodes (nodes A 1, B 2, C 3 and E 5 in this example) through which the idle path is passing. This path opening command is transmitted via the network management communication path indicated by the dotted chain line. Upon receiving this path opening command, these nodes (nodes A 1, B 2, C 3 and E 5) open the path to traffic as commanded, so as to realize the bandwidth increase.
The path number changing procedure at the network management system 6 is as shown in FIG. 3. Namely, when there is a new path allocation request (step 71), the network management system 6 carries out a route calculation for calculating traffic between nodes 1 and 2, traffic between nodes 2 and 3, and traffic between nodes 3 and 5, as well as a resource reservation for maintaining and confirming the currently used working paths while searching for idle paths (step 72), and if an idle path is found, the path set up is executed by transmitting the path opening command (path set up command) to nodes through which the idle path is passing (steps 73–75).
As indicated by three solid lines in FIG. 2, after the bandwidth increase, the number of working paths is increased by one, and a third protection path 3 is opened by transmitting the path opening command from the network management system 6 to a protection node 4 as indicated by three dashed lines in FIG. 2.
However, in the case of allocating a new path via the network management system, the search of idle resources in the network requires a considerable amount of time so that it is extremely difficult to set up a new path in response to an abrupt traffic variation.